This section provides information helpful in understanding the invention but that is not necessarily prior art.
Golf ball core and cover layers are typically constructed with polymer compositions including, for example, polybutadiene rubber, polyurethanes, polyamides, ionomers, and blends of such polymers. Ionomers, particularly ethylene-based ionomers, are a preferred group of polymers for golf ball layers because of their toughness, durability, and wide range of hardness values.
Golf ball compositions comprising highly neutralized acid polymers are known. For example, U.S. Pat. No. 7,375,151, the entire disclosure of which is incorporated herein by reference, discloses a highly-resilient thermoplastic ionomer resin composition comprising (a) melt-processable, ethylene acid copolymer; (b) aliphatic, mono-functional organic acid or its salt; (c) a thermoplastic resin; (d) a cation source; and (e) optionally, a filler. The ionomer resin may be neutralized to greater than 90% of all the acid groups present and remain melt-processable. The patent discloses using the highly-resilient thermoplastic composition in one-piece, two-piece, three-piece, and multi-layered golf balls.
Sullivan et al., U.S. Pat. No. 7,946,932 describes a golf ball with a fluid mass at its center enclosed in two mantle layers and a cover. The fluid center may be enclosed in a fluid center shell, which is preferably an elastomer with high temperature resistance. The fluid may be a gas, liquid, paste, foam, gel or reactive liquid that cures to a solid. Sullivan et al., U.S. Pat. No. 7,946,932 describes a similar golf ball having an outer core of with a layer of relatively soft HNP and a layer of relatively hard HNP.
Sullivan et al., US Patent Application Publication No. 2012/0122610 describes an inner core layer consisting essentially of a thermoplastic material and having a geometric center hardness greater than a surface hardness to define a negative hardness gradient. the thermoplastic material includes an ionomer, a highly-neutralized ionomer, a thermoplastic polyurethane, a thermoplastic polyurea, a styrene block copolymer, a polyester amide, polyester ether, a polyethylene acrylic acid copolymer or terpolymer, or a polyethylene methacrylic acid copolymer or terpolymer. The hardness gradient may be created by exposing the inner core layers to 1) a high-energy radiation treatment, such as electron beam or gamma radiation, 2) lower energy radiation, such as UV or IR radiation, 3) a solution treatment, such as an isocyanate or a silane; 4) incorporation of additional free radical initiator groups in the TP prior to molding; and/or 5) chemical modification, such as esterification or saponification.
While various uses for highly neutralized acid polymers in golf balls have been discovered, there is a need to improve golf ball materials using highly neutralized acid polymers or other thermoplastic polymers to particular golf ball constructions having desirable properties.